1. Field of the Invention
This invention pertains to improved polyblends as readily fabricatable synthetic plastic products which are such an admixed product of a copolymer of styrene and .alpha.-methylstyrene with a grafted interpolymerizate of polystyrene on an elastomeric polybutadiene substrate or backbone.
2. Description of the Prior Art
The preparations of various homo- and copolymers of .alpha.-methylstyrene including styrene/.alpha.-methylstyrene copolymers and many sorts of .alpha.-methylstyrene-containing graft, block and the like interpolymers on elastomeric or rubber substrates and/or with a number of other monomeric materials co- or otherwise interpolymerized with .alpha.-methylstyrene are well known and are exemplified in such references as U.S. Pat. Nos. 2,658,058, 3,036,053, 3,069,405, 3,367,995, 3,463,833, 3,825,623, 3,952,512, 3,956,426, 4,075,253, 4,097,557, 4,104,327, and 4,294,946 plus British Pat. No. 1,264,741 the teachings of which are incorporated by reference thereto.
The theory and practice of polymer compatibility and blending is set forth by D. R. Paul and Seymour Newman in Polymer Blends, Vols. 1 and 2, Academic Press (a Subsidiary of Harcourt Brace Jovanovich) Publishers of New York, San Francisco and London (1978), the context of which is incorporated by reference.
A number of plastics products, including polyblends, have been provided and are more or less well known, some of these including interpolymers of .alpha.-methylstyrene. Typical of these are: (a) the rubber-modified high impact styrene polymers in some of which mechanical blends of an elastomer with a polystyrene or other styrene copolymer are involved but in most the product is an at least partial interpolymer of styrene or mixtures of styrene and other monomeric materials copolymerizable therewith onto and with a polybutadiene or equivalent rubber or in combination with one or more synthetic, rubbery elastomers, (b) equivalents of the foregoing which are analogous but most frequently of a polyblend nature, including those in which the elastomeric component is an interpolymer of styrene, or in admixture with other monomer(s) copolymerizable with styrene made in graft-, block- or like or equivalent-interpolymer form with which a homo-or copolymer of styrene and/or other ethylenically-unsaturated monomeric materials that are copolymerizable by the free radical addition mode with styrene and like monomers is physically admixed for the resultant elastomer-modified product; and (c) the so-called ABS or ABS-type materials "ABS" being an acronym for interpolymers of acrylonitrile, butadiene and styrene) which have been available and used for many years and are characterized, in ABS Plastics by Costas H. Baskekis published in 1964 as part of its Plastics Application Series by Rheinhold Publishing Corporation of New York City, another being set forth in Toughened Plastics by C. B. Bucknell, Applied Science Publishers Ltd., London (1977); said publications being also herein incorporated by reference thereto.
Many of the polyblend products described in the foregoing in the item (b) materials are interblended products of styrene (and/or other monomeric materials which are copolymerizable with styrene) homo- and/or copolymer(s) that are not interpolymers with rubbers and/or elastomeric preformed polymers with the rubber- or other elastomer-modified grafted or the like (such as "block") interpolymers--and not merely mechanically blended--components identified amongst the item (a) products. A comprehensive capsulated description of the various types of graft- and/or block-copolymer varieties of interpolymerized elastomers is set forth in the disclosure of chemically-formulated or molecular architectural Structures (S-I) through (S-VI), inclusive, to be found in U.S. Pat. No. 4,371,663 (Russell), herewith incorporated by reference. There is a delineation of suitable natural and synthetic rubbers or elastomers useful for preparation of the here-contemplated graft-and/or block-type copolymer or interpolymer "backbones" or substrates as well as the actual grafted interpolymerized materials for utilization in the provision of the presently-involved polyblended products with styrene/ .alpha.-methylstyrene copolymers and their equivalents employed in practice of the present invention.
Many of the of synthetic resinous thermoplastic polymerizates and/or polyblends have acceptable tensile strengths, impact resistances and heat distortion values. However, they are often found to have less than desirable degrees of other significant properties such as and including thermal stability, hardness and environmental stress crack resistance; this being prevalent when the plastics are prepared from conventionally interpolymerizates of styrene, including the polyblends of various styrene polymers with differing rubber-modifiers.
It would be advantageous if a polyblend of a rubber-modifying styrene or the like graft copolymer components in intimate admixture with an .alpha.-methylstyrene or isopropenyl aromatic monomer were available which exhibited not only satisfactory properties of tensile strength, impact resistance and high heat distortion values but at the same time also displayed characteristics of superior thermal stability, outstanding hardness and environmental stress crack resistance to a superior degree.
These outstanding benefits and other advantages in accordance with the present invention can be understood from a consideration of the following specification and illustrations.